# Inhibition of Autophagy Reveals ATR Protein Kinase as a Key Mediator of Cisplatin Sensitivity in Osteosarcoma

## TL;DR

This study shows that blocking autophagy and ATR protein improves cisplatin effectiveness in osteosarcoma, potentially leading to better treatment outcomes.

## Contribution

The study identifies ATR as a novel upstream regulator linking DNA damage, autophagy, and chemoresistance in osteosarcoma.

## Key findings

- Higher autophagy levels correlate with worse outcomes in osteosarcoma tumors.
- ATG7 knockout enhances cisplatin sensitivity in HOS-143B cells by reducing p53 phosphorylation.
- ATR inhibition simultaneously disrupts DDR signaling and autophagy, increasing cell death in cisplatin-treated cells.

## Abstract

Osteosarcoma (OS) is the most common primary malignant bone tumor. Although the introduction of chemotherapy has improved the survival rate of OS patients, chemoresistance remains a major clinical problem underlying poor survival outcome. This study investigated the role of autophagy in OS chemoresistance and identified ATR as a novel upstream regulator linking DNA damage signaling, autophagy, and chemoresistance.

Elevated levels of autophagy were found in advanced grade and stage OS tumors, and higher autophagy levels were shown to be associated with poorer OS disease outcome. Chemotherapy significantly increased autophagy levels in HOS‐143B cells, while autophagy inhibition by autophagy‐related gene 7 knockout (ATG7

−/−

) significantly enhanced cisplatin (CIS) sensitivity in HOS‐143B cells. A kinase screen revealed a reduction in the phosphorylation of p53 (S15) in ATG7

−/−
HOS‐143B cells. ATR phosphorylates p53 at S15 responsible for DNA Damage Response (DDR), and ATR inhibition increased CIS sensitivity of HOS‐143B cells via apoptosis. Subsequent analysis verified that ATR inhibition decreased phosphorylation of p53 at S15 and blocked autophagy in CIS‐treated HOS‐143B cells.

These findings highlight ATR inhibition as a unique therapeutic strategy that simultaneously disrupts DDR signaling and autophagy, thereby enhancing CIS sensitivity. Targeting ATR could reduce the required CIS dosage, limit treatment‐associated toxicity, and ultimately improve survival and clinical outcomes for OS patients.

ATRi blocks phosphorylation of p53 (S15) and enhances cell death in cisplatin‐treated osteosarcoma cells.